1. Field of the Invention
The present invention relates to a method for forming an amorphous carbon film.
2. Description of the Related Art
A method for forming a carbon film on a metallic base material is well known. In a method for forming a film described in Japanese Unexamined Patent Application Publication No. 2004-270022, for example, a metallic base material is disposed on one of two electrodes in a chamber, and a carbon film having a hardness of 10 GPa or more is formed at an ambient pressure of 100 to 1600 Torr by applying a pulse voltage between the two electrodes and by supplying helium gas as a dilution gas and methane gas as a raw material gas such that the percentage of the methane gas relative to the helium gas is at a desired value.
Not only a carbon film having a hardness of 10 GPa or more but also a carbon film having a relatively low hardness of less than 10 GPa will have various applications. For example, such a carbon film is applicable to a coating used for sliding metal parts. In other words, since a carbon film having a relatively low hardness of less than 10 GPa is softer than a carbon film having a hardness of 10 GPa or more and accumulates less internal stress when a film is formed, such a carbon film can be formed on a material with a low elastic modulus such as aluminum and a thicker film can be achieved. If, for example, a one-atom layer of a coating is shaved off every time the coating is rubbed, such a thicker film has longer life. However, few methods for forming a carbon film having a relatively low hardness of less than 10 GPa has been proposed. In particular, a method for forming a carbon film at a pressure of more than 10 Torr and smaller than or equal to atmospheric pressure has not been proposed.